The present invention relates to a solid golf ball, and more particularly to a solid golf ball prepared from a rubber composition containing zinc acrylate coated with a higher fatty acid.
Golf balls are classified into two large groups, i.e. a solid golf ball and a wound golf ball. As a solid golf ball, there are known a one piece golf ball of a single structure, a two piece golf ball consisting of a solid core covered with a cover, and a golf ball of a multi-layer structure having three or more layers wherein an intermediate layer is provided between a core and a cover.
In general, a one piece golf ball and a core of a solid golf ball are prepared by heat pressure molding of a rubber composition containing a polybutadiene rubber, a radical initiator as a crosslinking or curing agent, e.g. a peroxide such as dicumyl peroxide, a metal salt of an unsaturated carboxylic acid as a co-crosslinking agent and zinc oxide used for controlling the weight of the golf ball. The unsaturated carboxylic acid metal salt is polymerized by means of the radical initiator such as a peroxide to produce hard reinforcing particles and link the reinforcing phase to the elastomeric phase by causing graft copolymerization of the monomer onto the polybutadiene in the interfacial region. Zinc acrylate has been preferably employed as a metal salt of unsaturated carboxylic acid.
Zinc acrylate is employed generally in a large quantity, for instance, 15 to 60 parts by weight per 100 parts by weight of polybutadiene rubber. Accordingly, zinc acrylate remarkably sticks to the roll surface upon kneading the rubber composition, thus the roll workability is remarkably lowered. Also, since zinc acrylate is easy to form agglomerates in the composition and poor in dispersibility, it is not effectively utilized. Consequently, the hardness of the ball becomes unexpectedly low or the impact resilience is not raised to the desired value, and the sound and feeling of striking the ball are bad.
It is an object of the present invention to provide a solid golf ball having a proper hardness, a good impact resilience, and good sound and feeling of striking.
Another object of the present invention is to provide a rubber composition suitable for preparing a one piece solid golf ball or a solid core for a solid golf ball and having a good processability such as roll workability and dispersibility of rubber additives.
These and other objects of the present invention will become apparent from the description hereinafter.